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Icom AH-4 Remote Automatic Antenna Tuner


The Icom AH-4 Remote Automatic Antenna Tuner is a very sophisticated remote antenna tuner. It is designed to interface with many modern Icom HF radios, but can be used with other radios using a third party interface adapter (more information below).

A good tuner of the near-the-radio (not remote) type is the LdgZ11ProTuner.

Why a Remote Tuner

Placing the antenna tuner very near to the antenna is very effective in minimizing losses if the antenna is far from resonance or presents an impedance different from the feedline. Coaxial feedlines become quite lossy at high standing wave ratios. Moving the tuner near the antenna allows the coaxial line to operate at or near 1:1 SWR. Balanced line feedlines exhibit much lower losses, but bringing them into the shack is often problematic. Even these low losses can be substantial in some cases and under some conditions (eg wet window line). Moving the tuner to the antenna makes the length of the balanced line minimal and reduces line losses.

The Icom AH-4 Tuner has a number of features that, in combination, differentiate it from others on the market. This combination makes the tuner work extremely predictably and reliably. Other tuners have some of these features, but none that I am aware of have all of them or combine them in the same fashion.

The Icom AH-4 has Excellent Customer Satisfaction

The Icom AH-4 Tuner enjoys extremely high customer ratings (see eHam link below). Why is the Icom Tuner so successful? Having owned and used a number of remote automatic antenna tuners myself, I think the Icom stands alone in trouble-free operation. While all others I have used will occasionally (or frequently) throw fits and jump out of tune, refuse to tune, etc., the Icom just works. I suspect Icom doesn't have a staff answering phonecalls about their tuner because of that. I've had trouble with other tuners and actually called the manufacturer (rare for me). They basically had a non-technical person answer the phone and explain how it was my fault that their tuner didn't work. They indicated that I didn't have enough radials (eventually I put out 500 feet of radials, quarterwaves on multiple bands, still had the problem). In their opinion, if their tuner would tune a light bulb then it was working. Their tuners do work some of the time, but my suspicion is that they just aren't properly designed to keep the RF out of the CPU, and they get confused in some circumstances. The AH-4 does not seem to have this problem. It has shielded enclosures inside, and by design it tunes only at low power. Once it has tuned it goes to sleep until you (or the radio) request it to tune again. No fuss, no muss.

Tuning a Light Bulb

Tuning a light bulb is an interesting test. Since the impedance changes with power and time, the tuner must re-tune in real time, and at full power, to properly deliver power to it. Most tuners will not tune a light bulb. Is this a problem? I submit that a proper antenna has an impedance that does not change with power. In this case tuning at low power works fine. Any antenna that changes impedance with power is nonlinear and probably broken. Tuning a light bulb does not generate the same RF field that tuning a real antenna does, and thus does not subject the tuner to the same RF stress. Thus the tuner that will successfully tune a light bulb and fail on a real antenna must be reacting to the different RF environment, and its subsequent failures to tune relate to that RF affecting the tuner in some inappropriate way. Note also that the manufacturer of the tuner I had trouble with makes another tuner of essentially the same schematic. The only difference is the size, this older model being about twice the length and width. This older model is reported to not have these problems, so I suspect that the proximity and placement of the components is related to the problem as well.

Icom AH-4 Power Consumption
The AH-4 does not use latching relays, so power is reuquired to maintain the relay configuration. This is typically a few hundred milliamps. The manufacturer rates the current draw as less than 2 amps, this should be a worst-case value. Once tuned the CPU shuts down so the remaining power consumption is dominated by the relays and drivers.

Icom AH-4 Feature Summary

Icom AH-4 Reviews

Icom AH-4 Summary Specifications

Compatible Icom Radios

Third Party Adapters for the Icom AH-4

I am testing the Better RF (link below) Yaesu FT100/857/897 Tune Control that interfaces to the Icom AH-4 Tuner. So far it has worked perfectly (for an hour), providing the signal for the AH-4 to tune when the Yaesu 'Tune' button is held for a second. This is very nice! I will continue to evaluate this device in the field and update this web page after I have some hours on the unit.

Tuner Interface Wiring and Protocol

The AH-4 uses a 4 conductor cable

The radio detects the presence of the tuner by checking for voltage on the start line. The tuner contains a pullup resistor from this line to +12 so if connected the radio detects this voltage.

...more to come

Comparisons with Other Remote Tuners

SGC 239 - I have already mentioned some of my experiences with the SGC 239 tuner. It tunes a light bulb well, and it tunes antennas well, but occasionally it 'goes crazy' and 'jumps out of tune'. (Usually right in the midst of a QSO). I have spoken to the factory about this (several years ago when the tuner was new) and they indicated that 'the counterpoise needed to be longer than the antenna, radials would not be enough'. I set up the tuner and antenna in many locations (portable) and put out different arrangements of up to 500 feet of radials or 250 feet of counterpoise for a 120 foot antenna. Still it happened. I used a battery to power the tuner. No help. One reliable way to solve the problem was to run 20 watts. That worked. 100 watts apparently is enough to occasionally confuse the tuner. I have heard from reliable sources that this problem does not occur with the SGC 230, which has essentially the same schematic as the 239, but is built in a much larger case. I suspect that RF is getting into the microprocessor in the 239 and causing problems. I have two of them, bought years apart, and they both do it, and they both tune light bulbs just fine, so I think it is a design problem rather than something broken. The AH-4's that I have do not seem to have problems. They just work, every time. Wish they would handle 500+ watts... Also, the Icom AH-4's are water-resistant, which the SGC 239 is not. The next tuner in the SGC line is the 237, which is also water-resistant, but it is more expensive than the AH-4.

RT-11 - I have an LDG RT-11 kit. It is mostly built, but not complete. At some point I will probably get back to that project and test it. The toroid wire cut chart seems to have some problems, so I have to straighten that out before I can finish the kit. The RT-11 has a water resistant case and uses latching relays which reduce power consumption. The matching range of the RT-11 is not as great as the AH-4, and the voltage and current ratings of latching relays is generally not as great as standard type relays. There is no pad for the transmitter, or automated setup to reduce transmitter power when tuning. The RT-11 is no longer made.

Icom AH-4 Cover Screws
One annoyance with the AH-4 is having to remove the case to terminate the cabling, and having to install a PL-259 on the coax after passing it through the entry into the case. It is nice to have the connections inside, however. It would be nice if they dispensed with the PL-259 for the coax, a couple of screw terminals would work fine and the eyelets could pass through the cable rubber entry and make the whole installation process easier.
Since the cover screws need to be removed, they can be lost. I lost two on Field Day one year, and found one of them the following year in the same spot. Never did find the other. But not a big problem. I found Stainless Steel equivalents and I'll get some replacements soon. Here's the info:

Other Resources

-- AlanB, WB6ZQZ

CategoryHamRadio CategoryRV

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